PD-L1 expression in malignant salivary gland tumors

Koji Harada, Tarannum Ferdous, Yoshiya Ueyama

Programmed death-1 ligand-1 (PD-L1) an important cancer biomarker that can suppress the immune system and its high expression is often reported to be related with increased tumor aggressiveness in some cancers. Here, we examined and evaluated PD-L1 expression in patients with malignant salivary gland tumor. Moreover, the relationship between PD-L1 immunolocalization and clinical pathological features, as well as the prognosis of malignant salivary gland tumors was investigated. We examined PD-L1expression in 47 patients with malignant salivary gland tumor by immunohistochemical staining. PD-L1 positivity was defined as ≥5% in tumor cell membrane and evaluated according to three categories (0% = 0, < 5% = 1, ≥5% = 2) in tumor-infiltrating mononuclear cells (TIMCs). Fisher's exact test was used to compare between PD-L1 expression and clinico-pathological features, and Kaplan-Meier method was used to estimate the distribution of OS by PD-L1 positivity. PD-L1 expression was detected in 51.1% of malignant salivary gland tumor tissues. No association was observed between PD-L1 immunolocalization in tumor and patient gender, or age. However, PD-L1 immunodetection of tumor cell membranes was significantly associated to stage, recurrence or metastasis after surgery, and patient outcome. On the other hand, PD-L1 immunodetection of tumor-infiltrating mononuclear cells (TIMCs) was significantly associated to recurrence or metastasis after surgery, and patient outcome. PD-L1 positivity in both tumor cell membrane and TIMCs was associated with shorter overall survival (OS) (p = 0.002 and p = 0.016, respectively). These findings suggested that patients with PD-L1 positive tumors or TIMCs appear to have poor clinical outcomes in malignant salivary gland tumors.